Fragility modeling of air-supported membrane roofs under unfavorable fire area growth: A time-based reliability approach

Air-supported membrane structures, characterized by complex roof geometry, diverse combustible layouts, and limited fire resistance, pose challenges to conventional fire analysis models and prescriptive fire protection design. This study develops a time-based fire fragility framework from the most adverse perspective to quantitatively assess membrane roof failure risk under localized fire exposure. The fire area growth rate (FAGR) is used as the fire intensity measure. Corner fire scenarios at three different membrane roof clearances are modeled by assigning FAGR values following a lognormal probability distribution based on actual fire data. The roof failure time corresponding to temperature-based membrane failure states is employed as the limit state indicator and associated with four performance levels. The simulations are conducted on a dual AMD EPYC 9654 system (192 cores, 2.8 GHz) with a total runtime of approximately 600 h. Results indicate that the transition between safe and failed states occurs within a relatively narrow range of FAGR under the uncertainty assumptions. Increasing the roof clearance above the fire area significantly raises the median FAGR, but the effect diminishes at higher performance levels. An approximately linear correlation is observed between critical roof failure temperature and median FAGR, with the slope governed by both roof clearance and performance level. In addition, larger structural dimensions also contribute to an increased median FAGR. The proposed framework provides a quantitative approach for assessing fire risk in air-supported membrane roofs and practical guidance for combustible material layout and roof protection strategies.